Hybrid acrylic star polymers with polysiloxane cores

ABSTRACT

Hybrid star polymers with acrylic arms and crosslinked polysiloxane cores can be made by a polycondensation of substituent alkoxysilyl groups contained in acrylic ester groups of acrylic block copolymers to form the cores.

BACKGROUND OF THE INVENTION

This invention concerns star polymers having acrylic arms andcrosslinked polysiloxane cores formed by condensation reactions of oneor more substituent alkoxysilyl functional groups attached to pendantester groups of the arms.

A. Aoki et al., U.S. Pat. No. 4,304,881 (1981), preparedstyrene/butadiene "living" polymers by anionic polymerization and thencoupled them by reaction with silicon tetrachloride to produce a 4-armstar polymer having a silicon atom as a core as shown in Example 4.

H. T. Verkouw, U.S. Pat. No. 4,185,042 (1980), prepared a polybutadiene"living" polymer by anionic polymerization and then prepared asilicon-containing star with up to 3.1 arms by reacting the "living"polymer with gamma-glycidoxypropyltrimethoxysilane.

O. W. Webster, U.S. Pat. Nos. 4,417,034 (Nov. 22, 1983) and 4,508,880(Apr. 2, 1985), and W. B. Farnham and D. Y. Sogah, U.S. Pat. Nos.4,414,372 (Nov. 8, 1983) and 4,524,196 (June 18, 1985) showed thatacrylic star polymers can be prepared via group transfer polymerizationby coupling "living" polymer with a capping agent having more than onereactive site or by initiating polymerization with an initiator whichcan initiate more than one polymer chain. Initiators that could produceacrylic star polymers with up to 4 arms were demonstrated.

H. J. Spinelli, in U.S. Pat. Nos., 4,659,782 and 4,659,783 issued Apr.21, 1987, teaches the preparation of acrylic star polymers withcrosslinked acrylic cores and at least 5 arms, optionally havingfunctional groups in the cores and/or the arms. Preferably GTPtechniques are used to make the polymers.

R. P. Zelinski et al. in U.S. Pat. No. 3,244,664 describe a three-stepprocess for coupling polymer chains involving (1) the preparation of anaddition polymer having one or two terminal alkali metal atoms on thepolymer main chain, or backbone, then (2) reacting the alkali metalatoms with certain silicic compounds to give a polymer productcontaining reactive silicon-containing terminal groups, and in whichreaction some coupling of molecules can occur, and then (3) furthertreatment of the product which can provide additional coupling. Thepolymers can be telechelic (a reactive group on each end of themolecule) or semi-telechelic (a reactive silicic group on only one end).Because of the nature of the process only one alkali metal atom, if any,and therefore only one silicon atom or one silicic group, can beattached directly to any one end of the polymer molecule. The singlesilicon group per end and the attachment to the end of the polymerbackbone limits the nature and extent of the subsequent coupling orcrosslinking possible among the molecules. Furthermore, thepolymerization process of the reference is subject to terminationreactions which result in some polymer chains being unable to react withthe silicon group and consequently unable to couple or crosslink at all.

An object of this invention is an improved hybrid star polymer comprisedof a crosslinked polysiloxane core with arms of linear acrylate and/ormethacrylate polymers.

SUMMARY OF THE INVENTION

This invention provides a hybrid star polymer comprised of a crosslinkedpolysiloxy core and attached thereto at least 4, preferably more than 4,polyacrylate and/or polymethacrylate arms, each arm being linked to atleast one silicon atom comprising the core by means of a chemical bondbetween a carbon atom contained in an ester group (i.e. alcoholate)portion of the acrylate and/or methacrylate arm polymer and said onesilicon atom of the core. By having the silicon group attached to apendant ester-forming group of the acrylic polymer chain, instead of tothe end of the polymer backbone itself, as in Zelinski U.S. Pat. No.3,244,664, a more stable arm polymer chain less subject to depropagationresults.

Such hybrid star polymers can be made by an improved process for thepreparation of a silicon-containing branched organic polymer includingthe steps of forming a linear addition arm polymer having a reactivemultifunctional silicon-containing group as a substituent in an endportion of the molecules thereof, and then reacting thesilicon-containing groups with each other to couple the polymermolecules with one another wherein the improvement comprises:

1) forming a linear acrylate and/or methacrylate block copolymer by agroup transfer polymerization process of acrylate and/or methacrylatemonomers in which one end of the copolymer molecules is formed using agroup transfer polymerization initiator, and/or a monomer or monomers,which contains as a substituent at least one crosslinkablepolyalkoxysilyl group and the other end of the molecule is formed usingan acrylate, and/or methacrylate initiator, monomer, and/or monomers,which contains no crosslinkable polyalkoxysilyl substituent; and then

2) crosslinking the alkoxysilyl groups with one another among thecopolymer molecules by a polycondensation reaction to form a copolymerhaving a crosslinked polysiloxy core and more than 4 linear polyacrylateand/or polymethacrylate arms attached thereto.

This invention also provides a linear block polyacrylate and/orpolymethacrylate copolymer comprised of two end portions and containingat least one reactive multifunctional crosslinkable silicon-containinggroup, such as a polyalkoxysilyl group, as a substituent in a pendantacrylate or methacrylate ester group in only one end portion of thepolymer molecule. By "copolymer" is meant a polymer chain having atleast one monomer unit, either as a final terminal monomer or beginninginitiator end unit, or somewhere else along the chain, which monomerunit contains said silicon containing substituent group. By "endportion" is meant not only the actual end units of the polymer chain,but also an end portion constituting less than half, preferably lessthan 20%, of the monomer units in the polymer chain, with the rest ofthe chain being free from said reactive silicon groups.

The star polymers can contain, on average, more than 10, but preferablyless than 500, arms per core.

The stars preferably have an M_(n) of at least 5000, and preferably from25,000 to 1,000,000 for better effectiveness when blended or mixed withother polymer systems.

The number of siloxy substituents per arm and their degree of reactionwith one another is selected to avoid gelation of the copolymer andprovide a star copolymer having a finite number average molecular weightin order to facilitate its processing and use in combination with otherpolymer systems.

DETAILED DESCRIPTION OF THE INVENTION

In the star polymer products of this invention the core contains atleast one silicon atom for each arm. The arms are attached to the coreby means of chemical bonds with one or more core silicon atoms. Theratio of core silicon atoms to the number of arms preferably is withinthe range of 1:1 to 8:1, and more preferably 2:1 to 5:1. Preferred armmolecular weights prior to the condensation reaction are in the range of1,000 to 20,000 number average molecular weight, Mn.

The arm block co-polymers can be prepared by a process in which the armpolymer is made to contain one or more silicon groups capable ofundergoing a condensation polymerization reaction with each other toform a crosslinked polysiloxane. The silicon groups are preferablycontained in one or more monomer units at or near one end of the armpolymer, or in a block of monomer units near one end of the arm polymermolecule. The monomer units containing the reactive silicon group may beadjacent to one another, or separated from one another randomly in ablock segment of the arm polymer. They may be located either at theinitiator end of the polymer chain or at the other end. However, whenthe initiator contains a reactive siloxy group, any other such groupsmust be at that end portion as well.

Preferably the reactive alkoxysilyl groups are located on the alcoholateportion of the ester groups in a segment of the arm polymer whichconsists of less than half of the monomer units of what the arm iscomprised, and preferably less than 20% of the arm units in order toachieve star formation with the desired core structure, while avoidinggelation and crosslinking of the copolymer in bulk to an infinitemolecular weight making it impossible to blend with other polymersystems.

Higher crosslinking density is achieved with one or more siliconcontaining polymer units at or adjacent to a terminal end of the armmolecule. A more open crosslink structure results when thesilicon-containing monomer units are separated from one another bynon-crosslinkable acrylate and methacrylate monomer units. In general,the more open the crosslink structure of the core, the greater thenumber of arms which can be condensed to form the core.

Arm polymers can be made by a group transfer polymerization (GTP)process preferably of the type taught in U.S. Pat. No. 4,417,043 toWebster and in U.S. Pat. No. 4,659,782 to Spinelli. The disclosures ofwhich are incorporated herein by reference.

The reactive core-forming silicon groups in the arm polymer prior tocrosslinking are attached to the ester portion of the acrylate ormethacrylate monomer as for example in 3-(trimethoxy)silylpropylmethacrylate; or in the GTP initiator such as in1-trimethylsiloxy-l(3-trimethoxysilyl)propoxy-2-methyl propene. Both ofthese can be used together as well.

The reactive silicon groups are preferably of the formula --Si--(OR)₃wherein R is hydrocarbyl, and preferably an aliphatic hydrocarbon groupcontaining up to 5 carbon atoms.

After preparation of the arm polymers, the living polymer is quenched toremove the living GTP groups and, simultaneously therewith orsubsequently, the crosslinkable silicon groups are crosslinked with oneanother by hydrolysis of the --OR groups to result in a crosslinkedsiloxane core structure. The term "crosslinkable" distinguishes thecore-forming silicon groups from the group transfer-initiating groupswhich contain silicon such as in a trimethylsiloxy initiator group asopposed to a trialkoxysilyl crosslinkable group.

The resulting star polymers may be used as formed in solution, ordispersion, or isolated for subsequent use.

The star polymers may be used as additives for liquid systems such asfor rheology control or for incorporation into other polymers and resinsystems to modify their properties.

The linear block copolymers of this invention are useful not only fordirect preparation of the hybrid star polymers of the invention byself-condensation reactions, but they also may be isolated andsubsequently condensed to form the star polymer in situ, for example ina film, or plastic sheet and so forth. In addition they can beco-reacted with other silicone-forming materials or suitablecondensation reactants to form other modified hybrid polymer systems forsubsequent processing and use, or in situ.

Preferably, for making the arms of star polymers of the invention, themonomers have one carbon-carbon double bond polymerizable by a grouptransfer polymerization process selected from ##STR1## and mixturesthereof wherein:

X is --CN, --CH═CHC(O)X' or --C(O)X';

Y is --H, --CH₃, --CN or --CO₂ R, provided, however, when X is--CH═CHC(O)X', Y is --H or --CH₃ ;

X' is --OSi(R¹)₃, --R, --OR or --NR'R";

each R₁ is independently selected from C₁₋₁₀ alkyl and C₆₋₁₀ aryl oralkaryl;

R is C₁° alkyl, alkenyl, or alkadienyl; C₆₋₂₀ cycloalkyl, aryl, alkarylor aralkyl; any of said groups containing one or more ether oxygen atomswithin aliphatic segments thereof; and any of all the aforesaid groupscontaining one or more functional substituents that are unreactive underpolymerizing conditions; and each of R' and R" is independently selectedfrom C₁₋ alkyl.

Also preferably in the preparation of arm polymers of the invention, the"living" group transfer polymerization, (GTP), sites are (R¹)₃ M--wherein: R¹ is selected from C₁ alkyl and C₆₋₁₀ aryl or alkaryl; and

M is Si, Sn, or Ge.

In particular, suitable GTP processes and their mechanism are describedin U.S. Pat. No. 4,659,782 at column 6, line 60 through column 9, line20 which is incorporated herein by reference.

As a preferred way to make hybrid star polymers of this invention, onefirst prepares acrylic arms by using a functional block copolymerprepared by GTP and then prepares a crosslinked, non-acrylic core byusing some type of polysiloxane condensation crosslinking reactioninvolving a segment of the starting GTP block copolymer which containsthe appropriate silicon group or groups. The self-stabilized particlewhich is thus produced has acrylic arms and a polysiloxane condensationcore (hence the name "hybrid") as opposed to stabilized star polymermolecules which have acrylic arms and acrylic cores.

The differences between all-acrylic stars and the subject hydrid starsare primarily associated with the polysiloxy condensation core. Thecondensation core obtained in the hybrid process is less acrylic innature than that produced in the all-acrylic process. Thus the swellingof the core or the sensitivity of the core to changes in solventcomposition may take on characteristics more resembling polysiloxanes.This aspect can be important in using the solubility difference tocontrol particle size during synthesis, and perhaps properties such asrefractive index after the particle was made, or hardness and softnessof the core depending on its crosslink density. The hardness/softness ofthe core can have an effect on impact resistance and toughness,especially when these hybrid stars are used in combination with varioustypes of acrylic and non-acrylic plastics.

The size, polarity and hardness of the condensation core can becontrolled by controlling the size of the starting functional segmenttogether with the amount, type and functionality of the crosslinkerwhich is used. The ability to use a previously isolated andcharacterized functional block copolymer, already containing thecrosslinkable substituent, as the starting material for a hybrid starcan be an advantage in that control over the final stabilized particleis not dependent on the existence of a "living" non-isolatedintermediate (e.g., attached and unattached arms). The sequential natureof the process--production of the functional block copolymer firstfollowed by formation of the stabilized particle--is important, however,it is not necessary to isolate the starting functional arm blockcopolymer in order to prepare a hybrid star, but isolation may sometimesprovide an advantage.

The nature and composition of the acrylic arms can be controlled andvaried as desired using the same techniques that are used for preparingthe functional segment of the block copolymers, or for the preparationof arms for all-acrylic stars.

Known uses of hydrocarbon stars together with the uses of all-acrylicstars are appropriate uses for the subject hybrid stars, with particularemphasis on the ability in the stars of this invention to control theparticle size, polarity and energy-absorbing nature (hardness/softness)of the condensation core and customize the star for the particular usedesired, in terms of compatibility and modification needed.

In addition to the uses of star polymers of the invention in coatingsand as tougheners for plastic sheeting and in the other applicationsindicated above, such star polymers have many other potential uses, asdo other products made by group transfer polymerization. These caninclude cast, blown, spun or sprayed applications in fiber, film, sheet,composite materials, multilayer coatings, photopolymerizable materials,photoresists, surface active agents including soil repellants andphysiologically active surfaces, adhesives, adhesion promoters andcoupling agents, among others. Uses include as dispersing agents,rheology control additives, heat distortion temperature modifiers,impact modifiers, reinforcing additives, stiffening modifiers andapplications which also take advantage of narrow molecular weight andlow bimodal polydispersity. End products taking advantage of availablecharacteristics can include lacquers, enamels, electrocoat finishes,high solids finishes, aqueous or solvent based finishes, clear or filledacrylic sheet or castings, including automotive and architecturalglazing and illumination housings and refractors, additives for oil andfuel, including antimisting agents, outdoor and indoor graphicsincluding signs and billboards and traffic control devices, reprographicproducts, and many others.

EXAMPLE 1 PMMA Star Made Using a Random Block of (Trialkoxy)-SilylpropylMethacrylate (DP3) and MMA

A 250 ml flask is equipped with mechanical stirrer, thermometer,nitrogen inlet, and addition funnels. The flask is charged withtetrahydrofuran (89.4 gm), methyl methacrylate (1.89 gm, 0.0189 mole),3-(trimethoxy)silylpropyl methacrylate (4.53 gm - 0.0183 mole), p-xylene(1.2 gm), bis(dimethylamino)methyl silane (0.56 gm), andtetrabutylammonium m-chlorobenzoate (60 ul of a 1.0M solution inacetonitrile). To this is added 1-trimethylsiloxy-1-methoxy-2-methylpropene (1.04 gm - 0.006 mole) initiator. This starts the polymerizationof the first block. A feed of tetrabutylammonium m-chlorobenzoate (60 ulof a 1.0M solution in acetonitrile) and terahydrofuran (4.1 gm) is thenstarted and added over 120 minutes. After 60 minutes, a feed of methylmethacrylate (57.55 gm, 0.576 mole) is started and added over 40minutes. This generates a linear polymer that has a block of MMA at oneend and a random block of MMA/3-(trimethoxy)silylpropyl methacrylate atthe other end. The monomers are 99.9% converted. The molecular weight ofthis polymer is Mn=9,600 and Mw=12,600.

To the polymer solution is added water (4.5 gm), methanol (2.0 gm), andtetrabutylammonium fluoride (0.25 ml of a 1.0M solution). This isrefluxed for 2 hours. This results in a solution of a hybrid starpolymer. The polymer has a cross-linked polysiloxane core, has aMn=77,600 and Mw=391,000 and an average of at least about 30 arms ofPMMA.

EXAMPLE 2 PMMA Star Made as in Example 1 with an Increased Amount ofSilylpropyl Methacrylate

A 250 ml flask is equipped with mechanical stirrer, thermometer,nitrogen inlet, and addition funnels. The flask is charged withtetrahydrofuran (90.5 gm), methyl methacrylate (1.75 gm, 0.0175 mole),3-(trimethoxy)silylpropyl methacrylate (7.33 gm - 0.0296 mole), p-xylene(1.2 gm), bis(dimethylamino)methyl silane (0.56 gm), andtetrabutylammonium m-chlorobenzoate (60 ul of a 1.0M solution inacetonitrile). To this is added 1-trimethylsiloxy-1-methoxy-2-methylpropene (0.97 gm - 0.056 mole). This starts the polymerization of thefirst block. A feed of tetrabutylammonium m-chlorobenzoate (60 ul of a1.0M solution in acetonitrile) and terahydrofuran (4.1 gm) is thenstarted and added over 120 minutes. After 60 minutes, a feed of methylmethacrylate (57.55 gm, 0.576 mole) is started and added over 40minutes. This generates a linear polymer that has a block of MMA and ablock of MMA/3-(trimethoxy)silylpropyl methacrylate. The monomers are99.9% converted. The molecular weight of this polymer is Mn =12,400 andMw =17,600.

To the polymer solution is added water (4.5 gm), methanol (2.0 gm), andtetrabutylammonium fluoride (0.25 ml of a 1.0M solution). This isrefluxed for 2 hours to quench the living polymer and to hydrolyze andcrosslink the alkoxy-silyl groups. A star polymer having a crosslinkedpolysiloxane core is formed that has a Mn=205,000 and Mw=5,166,000 andan average of about 300 arms.

EXAMPLE 2A

A 38 liter stirred autoclave was charged with 1.0 kg ethylene vinylacetate copolymer resin having a melt index of 2500 and a vinyl acetatecontent of 14 wt. %, 16 liters of carbon tetrachloride, and 4 liters ofchloroform. The autoclave was closed and the pressure was set at 0.21MPa. The reaction mixture was heated to 105° C. and held there until theresin dissolved; then addition of 2.7 ml/min initiator solution (1%2,2'-azobis-[2-methylpropane nitrile] in chloroform) was instituted.Chlorine gas was added to the reaction mixture at a rate of 7.7g/minutes. After chlorine had been added for 15 minutes, the reactiontemperature was lowered to 95° C. Chlorination was continued at constantcatalyst and chlorine feed rate for 6.25 hours. Following a degassingstep to remove the unreacted chlorine the autoclave was cooled anddischarged. The reaction mixture was filtered and the chlorinatedethylene vinyl acetate copolymer was isolated by drum drying. Elementalanalysis indicated that the polymer contained 58.5 wt. % chlorine. Thechlorinated polymer had a number average molecular weight of about12,000.

Coating compositions were prepared by mixing the materials shown inTable I, in the ratios indicated, with the binder composition ofchlorinated ethylene vinyl acetate, the branched polymethyl methacrylatesoluble acrylic star polymer and the plasticizers dioctyl phthalate andchlorinated paraffin. The composition was transferred to a ball mill andmixed for four days on a roller.

Film samples of the coating compositions were prepared by spraying themixed compositions shown in Table I with an air pressure pot at apressure of 4.5-9.0 kg onto unprimed cold rolled steel panels. Thepanels were air dried at room temperature for 24 hours and then vacuumdried at 50° C. for 72 hours before testing. The coating compositionswere evaluated for sprayability and film properties according to thetest methods described herein. Test results are summarized in Table.

                  TABLE I                                                         ______________________________________                                                           Example 2                                                  ______________________________________                                        Paint Composition                                                             Chlorinated Ethylene 15.15                                                    Vinyl Acetate (58.5% Cl)                                                      Star Polymethyl Methacrylate                                                                       1.52                                                     from Example 2                                                                "Chlorowax" LV.sup.1 3.64                                                     "Fluorad" 430 Fluoroaliphatic                                                                      0.13                                                     Polymeric Ester                                                               Barium Sulfate       7.84                                                     Titanium Oxide       12.17                                                    Magnesium Silicate, micronized                                                                     19.55                                                    Solvesso 100 Aromatic Solvent                                                                      6.00                                                     Xylene               5.00                                                     Toluene              1.78                                                     Methyl Ethyl Ketone  16.73                                                    Tetrahydrofuran      0.50                                                     Film Properties                                                               Tensile Strength, MPa                                                                              4.8                                                      Elongation at Break, %                                                                             20                                                       Chemical Resistance                                                           Acids (Avg.)         9.2                                                      Bases (Avg.)         8.7                                                      Solvents (Avg.)      6.6                                                      Chip Resistance      8                                                        Impact               A*        B**                                            40 lbs               10        10                                             80 lbs               10        10                                             120 lbs              10         9                                             160 lbs               9         9                                             ______________________________________                                         .sup.1 39 wt. % Cl, MW = 545                                                  *Concave                                                                      **Convex                                                                 

TEST METHODS

The following test methods were used:

Tensile Strength--ASTM D-412

Elongation at Break--ASTM D-412

Chemical Resistance--Unprimed cold rolled

Steel panels were coated with a binder composition containing pigmentand/or fillers in a solvent applied by spraying with an air pressure potat a pressure range between 4.5-9.0 kg. The panels were air dried atroom temperature for 24 hours and then vacuum dried at 50° C. for 48hours. For each chemical to be tested a 25 mm diameter circle was drawnon the panel and a drop of the chemical to be tested was placed withinthe circle. The drop was covered with a 2.5 cm plastic bottle lid toretard evaporation. After 24 hours at ambient temperature the lids wereremoved and the panels were washed with water to remove the testchemicals. After towel drying to remove surface residue, the panels wereair dried to 24 hours and evaluated according to the following scale:

10.0 No evidence of damage

8.0 Barely detectable spot

6.0 Definite spot, but no lifting

4.0 Glossing, discoloration, etching, slight lifting or slightblistering

2.0 Definite lifting or blistering Definite separation from substrate.

0.0 Dissolution or permanent removal of film by corrosive action.

Chip Resistance--A 10×30 cm cold rolled steel panel coated as describedin the chemical resistance test is held at 0° F. (-17.8° C.) for onehour. The air pressure in a QGR Gravelometer, (available from Q PanelCo., Cleveland, Ohio), is set at 70 psi (0.4MPa) and one pint of gravel,graded to a size 3/8-5/8 in. (0.95-1.59 cm, available from Q Panel Co.)preconditioned at 0° F. (-17.8° C.) is added to the gravelometer hopper.The steel panel is placed into the gravelometer and the gravel isprojected against the panel until the test is completed. The panel isthen rated on a scale of 0-10 with 10 being the highest rating toevaluate the amount of coating composition removed by the stones.

Impact Test--A coated steel panel coated as described in the chemicalresistance test is placed in a Gardner Impact Tester, (available fromPaul N. Gardner Co., P.O. Box 6633, Station 9, Fort Lauderdale, Fla.).The weighted steel rod is raised to different calibrated heights forspecific impact forces and released to impact against the panel. Bothconcave and convex impacts are determined on the coated side of thepanel. The panel is evaluated for impact resistance by inspection forsurface cracks and delamination on a scale of 0-10, with 10 being thehighest range.

Grid Hatch Adhesion--A coated cold rolled steel panel, prepared asdescribed in the chemical resistance test was scored with a series often paralle grooves 1 in. (2.54 cm) long and 0.1 cm apart with agridhatch adhesion scribe (available from Paul N. Gardner Co.). A secondseries of grooves is scribed at a 90° angle to the first series. A stripof "Scotch" brand #610 cellophane tape, 1 in. wide is applied to coverthe grid, leaving a 2 in. length of tape extending past the bottom ofthe grid. The tape is rubbed firmly with a pencil eraser. The tape isremoved by grasping the end and sharply pulling toward the tester,parallel to the coated surface, but not in a peeling fashion. Adhesionis rated by measuring the amount of film removed on a scale of 0-10,with 10 being the highest rating.

EXAMPLE 3 PMMA Star Made Using a Crosslinkable Silicon-ContainingInitiator as well as the Monomers of Examples 1 and 2

A 250 ml flask is equipped with mechanical stirrer, thermometer,nitrogen inlet, and addition funnels. The flask is charged withtetrahydrofuran (93.5 gm), methyl methacrylate (2.38 gm, 0.0238 mole),3-(trimethoxy)silylpropyl methacrylate (1.46 gm - 0.0059 mole), p-xylene(1.2 gm), bis(dimethylamino)methyl silane (0.56 gm), andtetrabutylammonium m-chlorobenzoate (60 ul of a 1.0M solution inacetonitrile). To this is added1-trimethylsiloxy-l-(3-trimethoxysilyl)propoxy-2-methyl propene (1.76gm - 0.0055 mole). This starts the polymerization of the first block. Afeed of tetrabutylammonium m-chlorobenzoate (60 ul of a 1.0M solution inacetonitrile) and terahydrofuran (4.1 gm) is then started and added over120 minutes. After 60 minutes, a feed of methyl methacrylate (57.2 gm,0.572 mole) is started and added over 40 minutes. This generates alinear polymer that has a block of MMA/3-(trimethoxy)silylpropylmethacrylate and then a block of MMA. The monomers are 99.9% converted.The molecular weight of this polymer is Mn=9,600 and Mw=11,500.

To the polymer solution is added water (3.0 gm), methanol (4.0 gm), andtetrabutylammonium fluoride (0.25 ml of a 1.0M solution). This isrefluxed for 2 hours. A solution of a star polymer is formed that has aMn=52,000 and Mw=186,000 and about 16 arms.

EXAMPLE 4 PMMA Star of Example 3 Using More Trimethoxy Silyl Monomer(DP3)

A 250 ml flask is equipped with mechanical stirrer, thermometer,nitrogen inlet, and addition funnels. The flask is charged withtetrahydrofuran (91.6 gm), methyl methacrylate (2.3 gm, 0.023 mole),3-(trimethoxy)silylpropyl methacrylate (4.6 gm - 0.0185 mole), p-xylene(1.2 gm), bis (dimethylamino)methyl silane (0.56 gm), andtetrabutylammonium m-chlorobenzoate (60 ul of a 1.0M solution inacetonitrile). To this is added 1-trimethylsiloxy-1-methoxy-2-methylpropene (1.75 gm - 0.0055 mole). This starts the polymerization of thefirst block. A feed of tetrabutylammonium m-chlorobenzoate (60 ul of a1.0M solution in acetonitrile) and terahydrofuran (4.1 gm) is thenstarted and added over 120 minutes. After 60 minutes, a feed of methylmethacrylate (56.5 gm, 0.565 mole) is started and added over 40 minutes.This generates a linear polymer that has a 3-(trimethoxy)silylpropylmethacrylate and then a block of MMA. The monomers are 99.9% converted.The molecular weight of this polymer is Mn= 10,300 and Mw=12,800.

To the polymer solution is added water (3.0 gm), methanol (4.0 gm), andtetrabutylammomnium fluoride (0.25 ml of a 1.0M solution). This isrefluxed for 2 hours. A star polymer is formed that has a Mn=129,000 andMw - 2,191,000 and about 170 arms per core.

EXAMPLE 5 PMMA Star Made Using a Block of the Silylpropyl Monomer (DP4)

A 250 ml flask is equipped with mechanical stirrer, thermometer,nitrogen inlet, and addition funnels. The flask is charged withtetrahydrofuran (91.0 gm), 3-(trimethoxy)silylpropyl methacrylate (5.68gm - 0.0229 mole), p-xylene (1.2 gm), bis(dimethylamino)methyl silane(0.30 gm), and tetrabutylammonium m-chlorobenzoate (80 ul of a 1.0Msolution of acetonitrile). To this is added1-trimethylsiloxy-1-methoxy-2-methyl propene (0.86 gm - 0.0049 mole).This starts the polymerization of the first block. A feed oftetrabutylammonium m-chlorobenzoate (80 ul of a 1.0M solution inacetonitrile) and terahydrofuran (4.1 gm) is then started and added over120 minutes. After 60 minutes, a feed of methyl methacrylate (53.45 gm,0.535 mole) is started and added over 40 minutes. This generates alinear polymer that has a block of MMA (DP 109) and a block of3-(trimethoxy)silylpropyl methacrylate. The monomers are 99.9%converted. The molecular weight of this polymer is Mn=11,600 and Mw=18,600.

To the polymer solution is added water (2.45 gm), methanol (4.0 gm), andtetrabutylammonium fluoride (0.5 ml of a 1.0M solution). This isrefluxed for 2 hours. A star polymer is formed that has a Mn=164,000 andMw=675,000 and about 36 arms per core of crosslinked polysiloxane.

EXAMPLE 6 MMA/EMA Star That Contains Hydroxyl Functionality and is MadeUsing a Random Block of Silylpropyl Methacrylate (DP5) and MMA in theArms for Crosslinking

A 500 ml flask is equipped with mechanical stirrer, thermometer,nitrogen inlet, and addition funnels. The flask is charged withtetrahydrofuran (73.4 gm), toluene (783.5 gm) methyl methacrylate (8.47gm, 0.085 mole), 3-(trimethoxy)silylpropyl methacrylate (24.67 gm -0.100 mole), p-xylene (1.2 gm), bis(dimethylamino)methyl silane (0.32gm), and tetrabutylammonium m-chlorobenzoate (200 ul of a 1.0M solutionin acetonitrile). To this is added 1-trimethylsiloxy-1-methoxy-2-methylpropene (3.23 gm - 0.0186 mole). This starts the polymerization of thefirst block. A feed of tetrabutylammonium m-chlorobenzoate (200 ul of a1.0M solution in acetonitrile) and terahydrofuran (4.1 gm) is thenstarted and added over 120 minutes. After 60 minutes, a feed of methylmethacrylate (71.7 gm, 0.717 mole) and ethyl methacrylate (74.5 gm,0.654 mole) is started and added over 40 minutes. Twenty minutes afterthe MMA/EMA feed is done 2-trimethylsiloxyethyl methacrylate (4.21 gm,0.0208 mole) is added in one shot. This generates a linear polymer thathas a block of MMA/3-(trimethoxy)silylpropyl methacrylate, a block ofMMA/EMA, and a block of 2-hydroxyethyl methacrylate which is blockedwith a trimethylsilyl group. The monomers are 99.9% converted. Themolecular weight of this polymer is Mn=9,800.

To the polymer solution is added water (15.3 gm), methanol (10.0 gm),i-propanol (36.6 gm), and tetrabutylammonium fluoride (0.6 ml of a 1.0Msolution). This is refluxed for 2 hours. This removes the blocking groupfrom the hydroxyethyl methacrylate and condenses the arms into a star. Astar polymer having a crosslinked polysiloxane core and about 25 armsper core is formed that has a Mn=62,400 and Mw=480,000. The star hashydroxyl groups located in a segment at the ends of the MMA/EMA arms.

EXAMPLE 6A

The following compositions can be prepared and then blended together toform a high solids white enamel.

    ______________________________________                                        Acrylic Polymer Solution 70.5                                                 (a polymer of styrene/methyl                                                  methacrylate/butyl acrylate/hydroxyethyl                                      acrylate 15/15/40/30 prepared at 75%                                          solids in methyl amyl ketone using                                            conventional free radical techniques)                                         Star Polymer (from Example 6)                                                                          25.0                                                 White Millbase           71.4                                                 (a standard millbase composed of 70%                                          white pigment, 10% acrylic polymer [from                                      the solution polymer described above]                                         and 20% methyl amyl ketone                                                    Melamine Resin           30.0                                                 P-toluene Sulfonic Acid Solution                                                                        2.8                                                 (17.7% P-toluene sulfonic acid, 12.5%                                         dimethyloxazolidine, and 69.8% methanol)                                      Xylene                   60.0                                                 Methyl Amyl Ketone       40.3                                                 Total                    300.0                                                ______________________________________                                    

The above composition is sprayed onto a steel panel primed with an alkydprimer and baked for 30 minutes at about 120° C. and gives a glossy,hard finish with a good appearance. The finish is resistant toweathering, solvents, scratches, and chips. The coating composition isuseful for finishing cars and trucks.

The above composition when sprayed and baked does not sag. Controls thatdo not contain any star polymer do gas when placed in the baking oven.The star polymer is useful in coatings.

EXAMPLE 7 PMMA Star with 2000 MW Arms and Made Using a TrialkoxysilylGroup only in the Initiator

A 250 ml flask is equipped with mechanical stirrer, thermometer,nitrogen inlet, and addition funnels. The flask is charged withtetrahydrofuran (61.6 gm), p-xylene (1.2 gm),1-trimethylsiloxy-1-3-(trimethoxysilyl)propoxy-2-methyl propene (9.65gm - 0.30 mole), and tetrabutylammonium m-chlorobenzoate (150 ul of a1.0M solution in acetonitrile). A feed of tetrabutylammoniumm-chlorobenzoate (150 ul of a 1.0M solution in acetonitrile) andterahydrofuran (4.1 gm) is then started and added over 120 minutes. Afeed of methyl methacrylate (60.1 gm, 0.601 mole) is started and addedover 40 minutes. This generates a linear polymer that has one3-(trimethoxy)silylpropoxy group at the end of a PMMA linear polymer.The monomers are 99.9% converted. The molecular weight of this polymeris Mn=1,900 and Mw=2,490.

To the polymer solution is added water (2.6 gm), methanol (4.0 gm), andtetrabutylammonium fluoride (0.25 ml of a 1.0M solution). This isrefluxed for 2 hours. A star polymer having a cross-linked polysiloxanecore is formed that has a Mn=8,250 and Mw=11,000 and an average of about4.4 arms per core.

EXAMPLE 8 PMMA Star with 10,000 MW Arms and Core Made Using Silicon onlyfor Crosslinking Initiator

A 250 ml flask is equipped with mechanical stirrer, thermometer,nitrogen inlet, and addition funnels. The flask is charged withtetrahydrofuran (61.6 gm), p-xylene (1.2 gm),1-trimethylsiloxy-1-3-(trimethoxysilyl)propoxy-2-methyl propene (1.98gm - 0.080 mole), and tetrabutylammonium m-chlorobenzoate (30 ul of a1.0M solution in acetonitrile). A feed of tetrabutylammoniumm-chlorbenzoate (30 ul of a 1.0M solution in acetonitrile) andterahydrofuran (4.1 gm) is then started and added over 120 minutes). Afeed of methyl methacrylate (60.9 gm, 0.609 mole) is started and addedover 40 minutes. This generates a linear polymer that has one3-(trimethoxy)silylpropoxy group at the end of a PMMA linear polymer.The monomers are 99.9% converted. The molecular weight of this polymeris Mn=10,600 and Mw=11,700.

To the polymer solution is added water (0.8 gm), methanol (1.3 gm), andtetrabutylammonium fluoride (0.03 ml of a 1.0M solution). This isrefluxed for 2 hours. A star polymer is formed that has a Mn=47,800 andMw=58,100 and an average of about 5 arms per core.

I claim:
 1. A hybrid star polymer comprised of a cross-linkedpolysiloxane core and attached thereto at least 4 linear polyacrylateand/or methacrylate arms, each arm being linked to at least one siliconatom comprising the core by means of a chemical bond between a carbonatom contained in an ester group portion of the acrylate and/ormethacrylate arm polymer and said one silicon atom of the core, saidstar polymer having a finite number average molecular weight.
 2. A starpolymer of claim 1 containing an average of from 5 to 500 arms.
 3. Astar polymer of claim 2 wherein the average ratio of core silicon atomsto arms is from 1:1 to 8:1.
 4. A star polymer of claim 2 wherein theaverage ratio of core silicon atoms to arms is from 2:1 to 5:1.
 5. Astar polymer of claim 1, 2 or 3 wherein the number average molecularweight of the arms is from 1,000 to 20,000.
 6. A star polymer of claim1, 2 or 3 wherein the number average molecular weight of the star isfrom 5,000 to 500,000.
 7. A star polymer of claim 1 or 2 wherein thearms consist essentially of poly(methyl methacrylate).
 8. A star polymerof claim 1 or 2 wherein the core is comprised of silicon atoms each ofwhich is bonded to a carbon atom which comprises an alkyl alcoholateester group of said polyacrylate or polymethacrylate.
 9. A star polymerof claim 1, 2 or 3 wherein the arms are derived from3-(trimethoxy)silylpropyl methacrylate.
 10. A star polymer of claim 1, 2or 3 wherein the arms are derived from the initiator1-trimethylsiloxy-1-(3-trimethoxysilyl)propoxy-2-methyl propene.
 11. Astar polymer of claim 3 wherein the arms are derived from3-(trimethoxy)silylpropyl methacrylate and from1-trimethylsiloxy-1-(3-trimethoxysilyl)propoxy-2-methyl propene.